Combination mathematical instrument



June 27, 1944- c. B. ALEXANDER 2,352,169

COMBINATION MATHEMATICAL INSTRUMENT Filed Dec. 7, 1943 CZQMM Mauddiwwk/z Fggfi. 1 7g] mewify/ vQ Patented June 27, 1944 ENTTJ Q CharlesBeltrand Alexa/rider,lllelbourneg v Victoria, Australia :7 I IApplication December 7, 1943;. Serial In Australia July 2,1942

No. 513,288 j 2 Claims. (oifssim This invention has been'devised withthe object of providing in a compact and durable form a combinationmathematical'instrument which will be found of great service andconvenience to draughtsmen in the architectural, engineering and alliedprofessions, as also to teachers and students at technical colleges andother educational establishments for the purpose of measuring and layingdown distances and angles on paper when engaged in drawing and plotting.

In the improved mathematical instrument there are combined a straightrule having a graduated scale on its surface; a protractor which isfitted to and is slidably adjustable longitudinally on the straightrule; a pointer adapted to be moved into register with the graduatedmarkings of the protractor; an angle rule the movements of which aresynchronous with those of the pointer, and means for securely holdingthe angle rule in the adjusted positions at which it is set.

Reference is made to the accompanying drawing which illustrates onepractical embodiment of the invention and wherein:

Fig. 1 is a view in plan of the improved combination mathematicalinstrument.

Fig. 2 is a side elevation of the same.

Fig. 3 is an underside plan of the instrument.

Fig. 4 is a view in plan on enlarged scale of the protractor from whichthe copper plate has been removed.

Fig. 5 is a plan view of the cover plate of the protractor.

Fig. 6 is a sectional view taken on the line 6-6 of Fig. 4.

Fig. 7 shows in side view the protractor with its cover plate inposition and illustrating the means for actuating the angle 'rule andthe pointer of the protractor.

In these views 2 designates a straight rule which is of suitable lengthand Width and is bevelled at 3 at its forward marginal portion toprovide a smooth, rigid edge 4 for guiding a pen or pencil in drawing orplotting. The bevelled portion of the rule has on its upper surface anappropriate scale indicated by 5, and at the right-hand side of saidbevelled portion there is an open-ended slot 6, the purpose of whichwill be hereinafter explained.

Formed longitudinally in the rule 2 closer to its front edge 4 than .toits rear edge 1 is an elongated slot 8 which is in parallelism with thesaid edge 4 and extends nearly the full length of the rule. The purposeof this elongated slot is to provide a guide'for aprotractor which ispermanently attached to the rule and 'is adapted to bea'djiis'td'thereon for being slidably moved in-a longitudinal direction.1 he protractor body 9 is" formed witha deep ital recess Itl to therebyprovide a raised mate-member I'l and-a 'fiathorizo'ntal portion dllwhereon isseated a bevelled arcuate member it which is fastenedconcentrically within the arcuate member -I lby means of rivets orws'IM'. Thearcuate member has on its surface-radial graduated: spacesand radial flin'e's with' markings-as customarily are provided onpro-tractors, and the bevelled arcuate member 13 has on its uppersurface a multiplicity of regularly spaced radial indentations, notshown in the drawing, which correspond with the radial lines marked onthe protractor member II. On the underside of the flat portion l2 of theprotractor body and preferably formed integrally therewith is a slideblock l5 which is fitted accurately and snugly within the guide slot 8of the straight rule 2.

The arcuate protractor member has an upward rim l5 at itsouter edge andthe chord of said member has an upward flange I! which is slightlyhigher than said rim to provide a seating for a cover plate l8 whichabuts against said flange and lies flush therewith. This cover plate hasa central hole I9 to facilitate its fixture when the components of theprotractor are being assembled and an arcuate slot 20 through which thegraduated spaces and markings of the protractor can be clearly read.

A hole 2| is formed through the fiat portion l2 of the protractor bodyand through the slide block l5 on the underside of said flat portion toserve as a bearing for a vertical spindle 22. This spindle isscrew-threaded exteriorly at its upper end portion 23 for engagementwith a knurled operating head 24, and it has a vertical tapped hole 25to threadedly engage a locking screw 26 passed through the tapped holein said knurled head.

A tapered protractor pointer 21 having at its outer end a centralindentation or line 28 is fixedly secured at its inner end onto thespindle 22 between a collar 29 and a collar 30 which latter is formedintegrally with the knurled head 24.

The pointer 21 is adapted to be moved across the upper surface of thearcuate protractor member II by manipulation of the knurled head 24 toimpart rotational movements in required direction to the spindle 22.Affixed to'the un;

derneath surface of the pointer is a spring claw 3| or the like which inthe movements of the pointer successively engages with a clicking soundthe radial indentations of the bevelled arcuate member l3 and therebygives an audible indication when the pointer is being moved or has beenmoved to a selected degree in the graduations appearing on theprotractor.

A discoid plate 32 is fixed onto the lower end of the spindle 22 so asto be rotatable therewith.

The said plate abuts against the underneath sur- I face of the rule 2and it is so dimensioned that it prevents accidental detachment of theslidably,

pose of maintaining the instrument slightly above the drawing paper andthus give sufficient clearance to ensure unrestricted slidable movementsof the protractor and free angular movements of the rule 34.

In the use of the instrument, the protractor is freely slid in eitherdirection to a required position on the straight rule 2, and rotationalmovement is imparted to the spindle 22 carrying the pointer 21 bymanipulation of the knurled operating head 24. Rotational movement ofthe spindle 22 imparts corresponding movement to the discoid plate 32 towhich the angle rule 34 is secured. When the said angle rule has beenmoved to the required angular position the knurled head 24 is turned byone hand while the: protractor is being held by the other hand. Thisknurled head is capable of slight rotational movement on the spindle 22and in consequence it can be turned to press upon the cover plate l8 andthereby clamp the said angle rule in the position at which it has beenset.

What I do claim is:

1. A combination mathematical instrument comprising, a straight rule, aprotractor slidably adjustable in longitudinal direction on said rule,

a protractor spindle, a pointer fast on said spindle adapted to registerwith the graduated markings on the protractor, a cover plate on saidprotractor, a knurled head threadedly engaging the upper end of saidspindle, and an angle rule fixedly connected't'o the opposite end ofsaid spindle, said knurled head having limited rotational movement onsaid spindle and adapted by pressing on said cover plate to exertclamping pressure upon said angle rule.

2. An improved combination mathematical instrument according to claim 1,wherein a discoid plate is fixed to the spindle of the protractor andthe angle rule is secured to said discoid plate.

CHARLES BELTRAND ALEXANDER.

